While a number of slit exposure type copying apparatuses employing various optical scanning means for scanning an original to be copied have been proposed, it is generally well known that when changing the magnification factor of the projected image, the conjugate distance must be changed or the projection lens must be replaced with another, and the speed of movement of the photosensitive member onto which an image of original is projected should be changed. Changes in the magnification factor become necessary when reproducing a set size of image from microfilm because the size of the frames vary because of differences in standards for microfilms. However, if the moving speed of photosensitive member is changed in accordance with the magnification, it becomes necessary to change the paper feeding speed, developing speed and so forth to correspond therewith, and because this is quite difficult and complicated, the more normal practice is to change the scanning speed of the optical scanning means, as shown in U.S. Pat. No. 3,614,222.
On the other hand, if the copying apparatus is the type in which the original to be copied is moved while the optical means is kept stationary, the speed of movement of the original may be changed instead of changing the speed of photosensitive member when there is a change of the magnification. However, if the original has an extremely small size, such as microfilm, the magnifying factor when enlarging is to be achieved is quite large, and the speed of movement of the microfilm is comparatively slow relative to the speed of the photosensitive member. Thus, in a case such as this, it is difficult to establish the proper relative speeds between the photosensetive member and microfilm if the magnification is to be changed.
To explain this in greater detail, reference is made to FIG. 1, in which a photosensitive member 1 in the form of a drum is rotated in the direction of the arrow at a velocity of V and the image of microfilm 3 is magnified by a projection lens 4 and projected through a slit 2 onto the photosensitive member 1 for forming an electrostatic latent image thereon. If the magnifying power of the lens 4 is to be M, then the microfilm may be moved at a speed of V/M in the direction opposite to the direction of rotation of the photosensitive member 1. However, since the magnification M of the microfilm 3 is large, such as on the order of 22, and if another projection lens 4' with a high magnifying power, such as on the order of 26, is substituted for the lens 4 to effect a change in magnification, the speed of movement of the microfilm 3 must be changed from 1/22 to 1/26 of the circumferential speed of the photosensitive member. Because this change of speed is normally effected by a reduction gear or by other suitable means, the speed of movement of film 3 tends to become inconsistent, thereby making the synchronization between the movement of the film 3 and that of the photosensitive member 1 difficult.
Thus, in order to change the magnification factor from M to M' to obtain a certain size of image, the lens 4 must be replaced with another lens 4' having a different focal length and also the speed of movement of the film 3 must be changed to V/M'. However, if V/M and V/M' are compared, the difference is quite small, and it is technically complicated to change the moving speed of film by a change in the power supplied to a driving motor. Similarly, to change the speed of movement of the film by gear means require separate sets of gears corresponding to each speed of movement, thereby making the system mechanically complicated.
As one solution to this problem, there has been proposed, in Japanese Published Examined Utility Model Application SHO No. 45-6456 published on Mar. 31, 1970, a copying apparatus as shown schematically in FIG. 2, in which a right angled mirror 6 is moved at one half the circumferential speed V of the photosensitive drum 7 for a distance l/2 which is half the length l of a stationary original 5. In this manner, the image of original is scanned and projected onto the drum 7 through the projection lens 4.
The arrangement shown in FIG. 2 operates basically on the same principle as the arrangement of FIG. 3 in which the original 5 to be copied is moved at a speed of v for a distance of l while the photosensitive drum 7 is moved at the circumferential speed of V. The relationship between the moving speed v of the original 5 and the circumferential speed V of the photosensitive drum 7 is V=Mv wherein M is the magnification power of lens 4. Accordingly, it is necessary to change either the moving speed v of original 5 or the circumferential speed V of photosensitive drum 7 to effect copying at another magnification. Thus, this system similarly requires a change of speed in accordance with the desired magnification, and it is technically difficult to establish the required speed the same as in other prior art devices.